Thermoplastic polyester compositions having improved impact properties

ABSTRACT

The present invention relates to thermoplastic polyesters, which comprise, by weight:
     (i) a thermoplastic polyester;   (ii) an impact modifier comprising:
       (a) a core-shell copolymer (A);   (b) an ethylene copolymer (B) chosen from ethylene-unsaturated carboxylic acid anhydride copolymers (B1), ethylene-unsaturated epoxide copolymers (B2) and blends thereof;   
       (iii) the (B)/(A) ratio being between 40/60 and 10/90 for proportions of impact modifier between 18 and 40% in 82 to 60% of polyester, respectively;   (iv) the (B)/(A) ratio being between 40/60 and 25/75 for proportions of impact modifier between 2 and 18% in 98 to 82% of polyester, respectively. It is particularly useful for PET and PBT.

FIELD OF THE INVENTION

The present invention relates to thermoplastic polyesters havingimproved impact properties and to impact-modifier compositions.

Thermoplastic polyesters, such as PBT (polybutylene terephthalate) andPET (polyethylene terephthalate) possess excellentdimensional-stability, heat-resistance and chemical-resistanceproperties and are used in the electrical, electronic and motor-vehiclefields. However, at high temperature, during conversion operations, areduction in the molecular weight of the polymer may occur, leading to areduction in the impact properties. In addition, polyesters have poorfracture-resistance properties in the case of notched components.

The present invention provides thermoplastic polymers in which animpact-modifier composition is added in order to obtain improved impactproperties, especially low-temperature toughness. The present inventionalso relates to this impact-modifier composition that is added to thepolyesters to improve the impact properties thereof. These modifiercompositions make it possible to achieve impact properties superior tothose obtained with each of the compounds separately.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,753,890 (=EP 174,343) describes polyesters, such as, forexample, polyethylene terephthalate (PET) or polybutylene terephthalate(PBT), which are modified by ethylene-alkyl(meth)acrylate-glycidyl(meth)acrylate copolymers.

U.S. Pat. No. 5,369,154 describes PET/polycarbonate blends containingfour different modifiers: a copolymer comprising an epoxide, a copolymerof the core-shell type, an SBR- or SBS- or EPR-type elastomer and acopolymer of the SAN or ABS type. These core-shell copolymers comprisefine particles having an elastomer core and a thermoplastic shell.

Patent EP 115,015 describes PET or PBT containing linear low-densitypolyethylene (LLDPE), glass fibres and optionally a core-shellcopolymer.

Patent EP 133,993 describes PET containing a core-shell copolymer and acopolymer of ethylene with either an alkyl acrylate or (meth)acrylicacid.

Japanese Patent Application JP 01,247,454 A, published on 3 Oct. 1989describes PBT containing an ethylene-alkyl(meth)acrylate copolymer andan ethylene-glycidyl methacrylate copolymer.

Patents EP 838,501 and EP 511,475 describe compositions similar to thoseof the above Japanese application.

Patent EP 803,537 describes PET and polycarbonate containing a copolymercomprising glycidyl methacrylate. Firstly, the polycarbonate and thecopolymer comprising glycidyl methacrylate are blended together and thenthis blend is incorporated into the PET.

Patent EP 187,650 describes PET containing a core-shell copolymer and acopolymer of ethylene with either maleic anhydride or a (meth)acrylicacid.

Patent EP 737,715 describes PBTs modified by an impact modifierconsisting of an ethylene-methyl methacrylate-glycidyl methacrylatecopolymer/core-shell copolymer blend. The amount of impact modifier isfrom 5 to 20 parts per 100 parts of polyester, i.e. 4.8 to 16.7% for95.2 to 83.7% of polyester, respectively. The proportions of theglycidyl methacrylate copolymer to the core-shell copolymer are in theratio 15/85 to 20/80. In the examples, the amount of impact modifier isfrom 18 parts per 100 parts of polyester, i.e. 15.3%, and the proportionof glycidyl methacrylate copolymer to the core-shell copolymer is in theratio 3/15, i.e. 17/83.

Patent EP 531,008 describes spent (recycled) PBT/polycarbonate (PC)blends containing core-shell copolymers, to which functionalizedcopolymers are added in order to make them into a new thermoplastic.These functionalized copolymers are either ethylene-glycidylmethacrylate (GMA) copolymers or ethylene-vinyl acetate-glycidylmethacrylate copolymers. The description quotes proportions of 1 to 97%of polycarbonate, from 1 to 97% of PBT, 1 to 40% of core-shell copolymerand 1 to 40% of glycidyl methacrylate copolymer. In fact, thePBT/polycarbonate blends that it is desired to recycle contain,according to the examples, 15% of core-shell copolymer, whichcorresponds to more realistic values. Blends (i) of 80 parts of recycledmaterial with 20 parts of glycidyl methacrylate copolymer and blends(ii) of 90 parts of recycled material with 10 parts of glycidylmethacrylate copolymer are then made. The proportions are in the EP531,008 table below, in which the parts are by weight:

TABLE EP 531 008 Compositions such that the core- shell copolymer/PC +PBT ratio = 15/85 PC + PBT 85 68 76.5 Core-shell copolymer 15 12 13.5(CS) GMA copolymer 20 10 PC + PBT + CS + 100 100 100 GMA copolymerGMA/CS copolymer 20/12 = (62/38) 10/13.5 = (43/57) Proportion ofmodifier 20 + 12 = 32% 10 + 13.5 = 23.5% (Core-shell copolymer + GMAcopolymer) in PC + PBT

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the Charpy Impact vs AX/Core Shellratio at −40° C.;

FIG. 2 is a diagram illustrating the Charpy Impact vs AX/Core Shellratio at +23° C.; and

FIG. 3 is a diagram illustrating the MFI vs AX/Core Shell ratio at 250°C.

It has been seen from the prior art that saturated polyesters can havetheir impact properties improved by the addition of a core-shellcopolymer. These polymers have a particularly well defined structure inwhich the core consists of a polymer having an elastomeric character andthe shell has a thermoplastic character. It has also been seen that theimprovement in impact strength may be obtained by also incorporating adispersed phase of an impact modifier optionally containing reactivefunctional groups capable of reacting with the functional groups of thepolyesters. This reactivity makes it possible to ensure a fine andhomogeneous dispersion of the modifier as well as good adhesion. Thecore-shell copolymer may itself also be functionalized in order to allowbetter adhesion to the matrix. However, this reactivity is sometimeshigh and may lead to a reduction in the melt flow index. This reductionin the melt flow index is prejudicial to the injection moulding of largeparts or of fine parts.

It has now been found that it is possible to improve the impactproperties of thermoplastic polyesters by adding two kinds of modifierto them, namely (a) a core-shell copolymer and (b) either anethylene-unsaturated epoxide copolymer or an ethylene-carboxylic acidanhydride copolymer, or a blend of these but in proportions in thepolyester and in (b)/(a) ratios which are different from those of theprior art EP 737,715 and EP 531,008. Better impact strength is obtained,while maintaining and even improving the melt flow index.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention relates to thermoplastic polyester compositionscomprising, by weight:

-   (i) a thermoplastic polyester;-   (ii) an impact modifier comprising:    -   (a) a core-shell copolymer (A);    -   (b) an ethylene copolymer (B) chosen from ethylene-unsaturated        carboxylic acid anhydride copolymers (B1), ethylene-unsaturated        epoxide copolymers (B2) and blends thereof;-   (iii) the (B)/(A) ratio being between 40/60 and 10/90 for    proportions of impact modifier between 18 and 40% in 82 to 60% of    polyester, respectively;-   (iv) the (B)/(A) ratio being between 40/60 and 25/75 for proportions    of impact modifier between 2 and 18% in 98 to 82% of polyester,    respectively, and advantageously between 5 and 18% in 95 to 82% of    polyester, respectively.

The present invention also relates to an impact-modifier compositionwhich can be added to the thermoplastic polyesters to improve theirimpact properties and comprising:

-   -   (a) a core-shell copolymer (A);    -   (b) an ethylene copolymer (B) chosen from ethylene-unsaturated        carboxylic acid anhydride copolymers (B1) and        ethylene-unsaturated epoxide copolymers (B2);    -   the (B)/(A) ratio being between 40/60 and 10/90 for proportions        of impact modifier between 18 and 40% in 82 to 60% of polyester,        respectively,    -   the (B)/(A) ratio being between 40/60 and 25/75 for proportions        of impact modifier between 2 and 18% in 98 to 82% of polyester,        respectively, and advantageously between 5 and 18% in 95 to 82%        of polyester, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The term “thermoplastic polyester” denotes polymers which are saturatedproducts coming from the condensation of glycols and of dicarboxylicacids, or of their derivatives. Preferably, they comprise the productsof the condensation of aromatic dicarboxylic acids having from 8 to 14carbon atoms and of at least one glycol chosen from the group consistingof neopentyl glycol, cyclohexanedimethanol and aliphatic glycols offormula HO(CH₂)_(n)OH in which n is an integer ranging from 2 to 10. Upto 50 mol % of the aromatic dicarboxylic acid may be replaced with atleast one other aromatic dicarboxylic acid having from 8 to 14 carbonatoms, and/or up to 20 mol % may be replaced with an aliphaticdicarboxylic acid having from 2 to 12 carbon atoms.

The preferred polyesters are polyethylene terephthalate (PET),poly(1,4-butylene) terephthalate (PBT), 1,4-cyclohexylene dimethyleneterephthalate/isophthalate) and other esters derived from aromaticdicarboxylic acids such as isophthalic acid, dibenzoic acid, naphthalenedicarboxylic acid, 4,4′-diphenylenedicarboxylic acid,bis(p-carboxyphenyl)methane acid, ethylene bis(p-benzoic) acid,1,4-tetramethylene bis(p-oxybenzoic) acid, ethylene bis(para-oxybenzoic)acid, 1,3-trimethylene bis(p-oxybenzoic) acid, and glycols such asethylene glycol, 1,3-trimethylene glycol, 1,4-tetramethylene glycol,1,6-hexamethylene glycol, 1,3-propylene glycol, 1,8-octamethylene glycoland 1,10-decamethylene glycol. The MFI of these polyesters, measured at250° C. and with 2.16 kg, may vary from 2 to 100 and advantageously from10 to 80. “MFI” denotes the melt flow index.

It would not be outside the scope of the invention if the polyestersconsisted of several diacids and/or several diols. It is also possibleto use a blend of various polyesters.

It would not be outside the scope of the invention if the polyesterscontained copolyetheresters. These copolyetheresters are copolymerscontaining polyester blocks and polyether blocks having polyether unitsderived from polyetherdiols such as polyethylene glycol (PEG),polypropylene glycol (PPG) or polytetramethylene glycol (PTMG),dicarboxylic acid units such as terephthalic acid units, and short,chain-extender, diol units such as glycol (ethanediol) or1,4-butanediol. The linking of the polyethers with the diacids forms theflexible segments whereas the linking of the glycol or butanediol withthe diacids forms the rigid segments of the copolyetherester. Thesecopolyetheresters are thermoplastic elastomers. The proportion of thesecopolyetheresters may represent up to 30 parts per 100 parts ofthermoplastic polyester.

It would not be outside the scope of the invention if the polyesterscontained polycarbonate. In general, the term “polycarbonate” denotespolymers comprising the following units:

in which R₁ is an aliphatic, alicyclic or aromatic divalent group; thealiphatic and alicyclic groups may contain up to 8 carbon atoms. By wayof example of R₁, mention may be made of ethylene, propylene,trimethylene, tetramethylene, hexamethylene, dodecamethylene,poly(1,4-[2-butenylene]), poly(1,10-[(2-ethyldecylene]),1,3-cyclopentylene, 1,3-cyclohexylene, 1,4-cyclohexylene, m-phenylene,p-phenylene, 4,4′-diphenylene, 2,2-bis(4-phenylene)propane andbenzene-1,4-dimethylene. Advantageously, at least 60% of the R₁ groupsin the polycarbonate and preferably all the groups R₁ are aromaticgroups of formula:

in which R₂ et R₃ are divalent monocyclic aromatic radicals and Y is alinking radical in which one or two atoms separate R₂ and R₃. The freevalences are generally in the meta or para position with respect to Y.R₂ and R₃ may be substituted or unsubstituted phenylenes; assubstituents, mention may be made of alkyl, alkenyl, halogen, nitro andalkoxy. Preferably, the phenylenes are unsubstituted; they may betogether or separately meta or para and are preferably para. The linkingradical Y is preferably such that one atom separates R₂ from R₃ and ispreferably a hydrocarbon radical such as methylene, cyclohexylmethylene,2-[2.2.1]bicycloheptylmethylene, ethylene, 2,2-propylene,1,1-(2,2-dimethylpropylene), 1,1-cyclohexylene, 1,1-cyclopentadecylene,cyclododecylene, carbonyl, the oxy radical, the thio radical andsulfone. Preferably, R₁ is 2,2-bis(4-phenylene)propane which comes frombisphenol A, that is to say Y is isopropylidene and R₂ and R₃ are eachp-phenylene. Advantageously, the intrinsic viscosity of thepolycarbonate, measured in methylene chloride at 25° C., is between 0.3and 1 dl/g.

The proportion of polycarbonate may represent up to 30 parts per 100parts of thermoplastic polyester.

With regard to the core-shell copolymer (A), this is in the form of fineparticles having an elastomer core and at least one thermoplastic shell,the particle size being generally less than 1 μm and advantageouslybetween 200 and 500 nm. By way of example of the core, mention may bemade of isoprene homopolymers or butadiene homopolymers, copolymers ofisoprene with at most 30 mol % of a vinyl monomer and copolymers ofbutadiene with at most 30 mol % of a vinyl monomer. The vinyl monomermay be styrene, an alkylstyrene, acrylonitrile or analkyl(meth)acrylate. Another core family consists of the homopolymers ofan alkyl (meth)acrylate and the copolymers of an alkyl(meth)acrylatewith at most 30 mol % of a vinyl monomer. The alkyl(meth)acrylate isadvantageously butyl acrylate. The vinyl monomer may be styrene, analkylstyrene, acrylonitrile, butadiene or isoprene. The core of thecopolymer (A) may be completely or partly crosslinked. All that isrequired is to add at least difunctional monomers during the preparationof the core; these monomers may be chosen from poly(meth)acrylic estersof polyols, such as butylene di(meth)acrylate and trimethylolpropanetrimethacrylate. Other difunctional monomers are, for example,divinylbenzene, trivinylbenzene, vinyl acrylate and vinyl methacrylate.The core can also be crosslinked by introducing into it, by grafting oras a comonomer during the polymerization, unsaturated functionalmonomers such as anhydrides of unsaturated carboxylic acids, unsaturatedcarboxylic acids and unsaturated epoxides. Mention may be made, by wayof example, of maleic anhydride, (meth)acrylic acid and glycidylmethacrylate.

The shell(s) are styrene homopolymers, alkylstyrene homopolymers ormethyl methacrylate homopolymers, or copolymers comprising at least 70mol % of one of the above monomers and at least one comonomer chosenfrom the other above monomers, vinyl acetate and acrylonitrile. Theshell may be functionalized by introducing into it, by grafting or as acomonomer during the polymerization, unsaturated functional monomerssuch as anhydrides of unsaturated carboxylic acids, unsaturatedcarboxylic acids and unsaturated epoxides. Mention may be made, forexample, of maleic anhydride, (meth)acrylic acid and glycidylmethacrylate. By way of example, mention may be made of core-shellcopolymers (A) having a polystyrene shell and core-shell copolymers (A)having a PMMA shell. There are also core-shell copolymers (A) having twoshells, one made of polystyrene and the other, on the outside, made ofPMMA. Examples of copolymers (A) and their method of preparation aredescribed in the following patents: U.S. Pat. No. 4,180,494, U.S. Pat.No. 3,808,180, U.S. Pat. No. 4,096,202, U.S. Pat. No. 4,260,693, U.S.Pat. No. 3,287,443, U.S. Pat. No. 3,657,391, U.S. Pat. No. 4,299,928 andU.S. Pat. No. 3,985,704.

Advantageously, the core represents, by weight, 70 to 90% of (A) and theshell represents 30 to 10%.

By way of example of a copolymer (A), mention may be made of thatconsisting (i) of 75 to 80 parts of a core comprising at least 93 mol %of butadiene, 5 mol % of styrene and 0.5 to 1 mol % of divinylbenzeneand (ii) of 25 to 20 parts of two shells essentially of the same weight,the inner one made of polystyrene and the outer one made of PMMA.

With regard to ethylene-unsaturated carboxylic acid anhydride copolymers(B1), these may be polyethylenes grafted by an unsaturated carboxylicacid anhydride or ethylene-unsaturated carboxylic acid anhydridecopolymers which are obtained, for example, by radical polymerization.

The unsaturated carboxylic acid anhydride may be chosen, for example,from maleic, itaconic, citraconic, allylsuccinic,cyclohex-4-ene-1,2-dicarboxylic,4-methylenecyclohex-4-ene-1,2-dicarboxylic,bicyclo-[2.2.1]hept-5-ene-2,3-dicarboxylic andx-methylbicyclo[2.2.1]hept-5-ene-2,2-dicarboxylic anhydrides.Advantageously, maleic anhydride is used. It would not be outside thescope of the invention to replace all or part of the anhydride with anunsaturated carboxylic acid such as, for example, (meth)acrylic acid.

With regard to the polyethylenes onto which the unsaturated carboxylicacid anhydride is grafted, the term “polyethylene” should be understoodto mean homopolymers or copolymers.

By way of comonomers, mention may be made of:

alpha-olefins, advantageously those having from 3 to 30 carbon atoms; byway of examples of alpha-olefins, mention may be made of propylene,1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene,3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene,1-hexadecene, 1-octadecene, 1-eicocene, 1-dococene, 1-tetracocene,1-hexacocene, 1-octacocene and 1-triacontene; these alpha-olefins may beused separately or as a mixture of two or more of them;

esters of unsaturated carboxylic acids, such as, for example, alkyl(meth)acrylates, the alkyls possibly having up to 24 carbon atoms;examples of alkyl acrylates or methacrylates are especially methylmethacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and2-ethylhexyl acrylate;

vinyl esters of saturated carboxylic acids, such as, for example, vinylacetate or vinyl propionate;

dienes such as, for example, 1,4-hexadiene.

The polyethylene may include several of the above comonomers.

Advantageously, the polyethylene, which may be a blend of severalpolymers, comprises at least 50 mol % and preferably 75 mol % ofethylene and its density may be between 0.86 and 0.98 g/cm³. The MFI(Melt Flow Index at 190° C./2.16 kg) is advantageously between 0.1 and1000 g/10 min. By way of example of polyethylenes, mention may be madeof:

low-density polyethylene (LDPE)

high-density polyethylene (HDPE)

linear low-density polyethylene (LLDPE)

very low-density polyethylene (VLDPE)

polyethylene obtained by metallocene catalysis, that is to say polymersobtained by the copolymerization of ethylene and of an alpha-olefin suchas propylene, butene, hexene or octene in the presence of a single-sitecatalyst generally consisting of a zirconium or titanium atom and of twoalkyl cyclic molecules linked to the metal. More specifically, themetallocene catalysts are usually composed of two cyclopentadiene ringslinked to the metal. These catalysts are frequently used withaluminoxanes as cocatalysts or activators, preferably methylaluminoxane(MAO). Hafnium may also be used as the metal to which thecyclopentadiene is fixed. Other metallocenes may include transitionmetals of Groups IV A, V A and VI A. Metals from the series oflanthamides may also be used.

EPR (ethylene-propylene-rubber) elastomers;

EPDM (ethylene-propylene-diene) elastomers;

blends of polyethylene with an EPR or an EPDM;

ethylene-alkyl(meth)acrylate copolymers possibly containing up to 60%,and preferably 2 to 40%, by weight of (meth)acrylate.

The grafting is an operation known per se.

With regard to the ethylene-unsaturated carboxylic acid anhydridecopolymers, that is to say those in which the unsaturated carboxylicacid anhydride is not grafted, these are copolymers of ethylene, theunsaturated carboxylic acid anhydride and, optionally another monomerwhich may be chosen from the comonomers that were mentioned above in thecase of the ethylene copolymers intended to be grafted.

Advantageously, ethylene-maleic anhydride copolymers and ethylene-alkyl(meth)acrylate-maleic anhydride copolymers are used. These copolymerscomprise from 0.2 to 10% by weight of maleic anhydride and from 0 to40%, preferably 5 to 40%, by weight of alkyl(meth)acrylate. Their MFIsare between 0.5 and 200 (190° C./2.16 kg). The alkyl(meth)acrylates havealready been described above. It is possible to use a blend of severalcopolymers (B1), and it is also possible to use an ethylene-maleicanhydride copolymer/ethylene-alkyl(meth)acrylate-maleic anhydridecopolymer blend.

The copolymer (B1) is commercially available, produced by radicalpolymerization at a pressure which may range between 200 and 2500 barand is sold in the form of granules.

With regard to the ethylene-unsaturated epoxide copolymers (B2), thesemay be obtained by the copolymerization of ethylene with an unsaturatedepoxide or by grafting the unsaturated epoxide to the polyethylene. Thegrafting may be carried out in the solvent phase or onto thepolyethylene in the melt in the presence of a peroxide. These graftingtechniques are known per se. With regard to the copolymerization ofethylene with an unsaturated epoxide, it is possible to use so-calledradical polymerization processes usually operating at pressures between200 et 2500 bar.

By way of example of unsaturated epoxides, mention may be made of:

aliphatic glycidyl esters and ethers, such as allyl glycidyl ether,vinyl glycidyl ether, glycidyl maleate, glycidyl itaconate, glycidylacrylate and glycidyl methacrylate; and

alicyclic glycidyl esters and ethers, such as 2-cyclohex-1-ene glycidylether, diglycidyl cyclohexene-4-5-dicarboxylate, glycidylcyclohexene-4-carboxylate, glycidyl 2-methyl-5-norbornene-2-carboxylateand diglycidyl endo-cis-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate.

With regard to grafting, the copolymer is obtained by grafting anethylene homopolymer or copolymer as described in the case of (B1),except that an epoxide is grafted instead of an anhydride. With regardto copolymerization, this is also similar to (B1) except that an epoxideis used; it may also have other comonomers, as in the case of (B1).

The product (B2) is advantageously anethylene-alkyl(meth)acrylate-unsaturated epoxide copolymer or anethylene-unsaturated epoxide copolymer. Advantageously, it may containup to 40%, preferably 5 to 40%, by weight of alkyl(meth)acrylate and upto 10%, preferably 0.1 to 8%, by weight of unsaturated epoxide.

Advantageously, the epoxide is glycidyl(meth)acrylate.

Advantageously, the alkyl(meth)acrylate is chosen from methyl(meth)acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and2-ethylhexyl acrylate. The amount of alkyl(meth)acrylate isadvantageously from 20 to 35%. The MFI is advantageously between 0.5 and200 (in g/10 min. at 190° C./2.16 kg). It is possible to use a blend ofseveral copolymers (B2), and it is also possible to use anethylene-alkyl (meth)acrylate-unsaturated epoxidecopolymer/ethylene-unsaturated epoxide copolymer blend. It is alsopossible to use blends of (B1) and (B2).

This copolymer (B2) may be obtained by radical polymerization of themonomers.

Advantageously, the thermoplastic polyester compositions of theinvention comprise, per 100 parts by weight, 75 to 95 parts of polyesterfor 25 to 5 parts of impact modifier, respectively.

Advantageously, the proportions of (A) and (B) are such that the (B)/(A)ratio is between 40/60 and 25/75, whatever the amount of impact modifierin the polyester.

Among the copolymers (B), it is advantageous to use the copolymers (B2).

The invention also relates to an impact-modifier composition havingthese proportions.

The thermoplastic polyesters of the invention may also include, inaddition to the impact modifier, slip agents, antiblocking agents,antioxidants, UV stabilizers and fillers. The fillers may be glassfibres, fire retardants, talc or chalk.

The thermoplastic polyester/impact-modifier blends are prepared by theusual techniques for thermoplastic polymers in single-screw ortwin-screw extruders, mixers or apparatuses of the BUSS® Ko-kneadertype. The polyester and the constituents of the impact modifier, namelythe copolymers (A), (B) and (C), may be introduced separately into theblending device. The constituents of the impact modifier may also beadded in the form of a blend prepared in advance, possibly in the formof a masterbatch in the polyester. The additives may be added into theseapparatuses, such as the slip agents, the antiblocking agents, theantioxidants, the UV stabilizers and the fillers, whether as they are orin the form of a masterbatch in the polyester or else in the form of amasterbatch with one or more of the copolymers (A) to (C). Theimpact-modifier composition comprising (A) to (C) which may be added tothe polyesters is also prepared by the previous usual technique ofblending thermoplastic polymers.

EXAMPLES

The following products were used:

AX 8900: ethylene-methyl acrylate-glycidyl methacrylate (GMA) copolymercomprising, by weight, 25% acrylate and 8% GMA, having an MFI of 6 (190°C./2.16 kg). It is sold under the brand name LOTADER® par Elf Atochem;

AX 8930: ethylene-methyl acrylate-glycidyl methacrylate (GMA) copolymercomprising, by weight, 25% acrylate and 3% GMA, having an MFI of 6 (190°C./2.16 kg). It is sold under the brand name LOTADER® par Elf Atochem;

E920: MBS-type core-shell copolymer with a core essentially based onbutadiene-styrene and a shell of PMMA, sold by Elf Atochem under thebrand name METABLEND®;

EXL 2314: epoxy-functionalized acrylic core-shell copolymer sold by Röhmand Haas under the brand name PARALOID®;

PBT: polybutylene terephthalate having an MFI of 20 (250° C./2.16 kg)sold by BASF under the brand name ULTRADUR® B4500.

All the examples were produced with compositions comprising 80% byweight of PBT and 20% by weight of impact modifier. The notched Charpyimpact strength complies with the ISO 179:93 standard; the higher thevalue the better the impact strength.

FIG. 1 shows the notched Charpy impact strength at −40° C. for PBTcontaining impact modifier consisting either of AX or of core-shellcopolymer or of their blends. Two kinds of AX: AX 8900 and AX 8930 andtwo kinds of core-shell copolymer: EXL 2314 and E920 were used. FIG. 2shows the impact strengths of these same compositions at +23° C. Inthese figures and in the tables, the epoxide copolymer has been denotedby AX and the core-shell copolymer by CS. The AX/CS ratio is the weightratio, “30/70” meaning 30 parts of AX to 70 parts of CS. The values arealso given in TABLE 1 and TABLE 2.

TABLE 1 PBT + 20%(AX + CS) AX = AX 8900 or AX Notched Charpy impactstrength at −40° C. 8930 CS = EXL 2314 or AX 8900 AX 8900/ AX 8930 AX8930/ E920 EXL 2314 E920 EXL 2314 E920 100/0 AX/CS 6.2 6.2 5 5(comparative) 70/30 AX/CS 9.8 10 8.8 9.9 (comparative) 30/70 AX/CS 7.814.75 7.1 9.8 20/80 AX/CS 9.2 10.25 10/90 AX/CS 13.8 0/100 AX/CS 6.758.2 6.75 8.2 (comparative)

TABLE 2 PBT + 20%(AX + CS) AX = AX 8900 or AX Notched Charpy impactstrength at +23° C. 8930 CS = EXL 2314 or AX 8900 AX 8900/ AX 8930 AX8930/ E920 EXL 2314 E920 EXL 2314 E920 100/0 AX/CS 76.4 76.4 55.2 55.2(comparative) 70/30 AX/CS 99 62.2 67.5 61 (comparative) 30/70 AX/CS 91.888.9 82.6 88.4 20/80 AX/CS 87.6 79.5 10/90 AX/CS 80 0/100 AX/CS 62 18 6218 (comparative)

FIG. 3 shows the MFI of the above compositions containing the variousimpact modifiers and also the MFI of the PBT without a modifier: “purePBT”. The values are also given in TABLE 3 below.

TABLE 3 PBT + 20%(AX + CS) AX = AX 8900 or AX 8930 MFI (250° C./2.16 kg)CS = EXL 2314 or E920 no change with the type of AX and CS 100/0 AX/CS(comparative) 0.63 70/30 AX/CS (comparative) 0.9 30/70 AX/CS 1.63 20/80AX/CS 3.5 10/90 AX/CS 3 0/100 AX/CS (comparative) 7.4 Pure PBT(comparative) 20

It is within the skill in the art to practice this invention in numerousmodifications and variations in light of the above teachings. Therefore,it is understood that the various embodiments of this inventiondescribed herein may be altered without departing from the spirit andscope of this invention as defined by the appended claims.

1. Thermoplastic polyester compositions comprising, by weight: (i) from60 to 98% by weight of a thermoplastic component consisting of athermoplastic polyester; and (ii) from 2 to 40% by weight of an impactmodifier consisting of: (a) a core-shell copolymer (A) having a singleshell; wherein the core consists of one or more polymers selected fromthe group consisting of isoprene homopolymers, copolymers of isoprenewith at most 30 mol % of a vinyl monomer selected from the groupconsisting of styrene, alkylstyrene and alkyl(meth)acrylate, copolymersof butadiene with at most 30 mol % of an alkyl(meth)acrylate, andcopolymers of alkyl(meth)acrylate with more than 0 mol % and at most 30mol % of a vinyl monomer selected from the group consisting of styreneand alkylstyrene; further wherein the shell consists of one or morepolymers selected from the group consisting of styrene homopolymers,alkylstyrene homopolymers, methyl methacrylate homopolymers, andcopolymers consisting of at least 70 mol % of a styrene, alkyl styreneor methyl methacrylate with at most 30 mol % of a vinyl acetate; and (b)an ethylene copolymer (B) chosen from ethylene-unsaturated epoxidecopolymers (B2); (iii) the (B2)/(A) ratio being between 40/60 and 10/90for proportions of impact modifier between 18 and 40% in 82 to 60% ofpolyester, respectively; (iv) the (B2)/(A) ratio being between 40/60 and25/75 for proportions of impact modifier between 2 and 18% in 98 to 82%of polyester, respectively.
 2. Compositions according to claim 1,wherein the polyester is selected from PET and PBT.
 3. Compositionsaccording to claim 1, comprising up to 30 parts by weight ofcopolyetherester per 100 parts of thermoplastic polyester. 4.Compositions according to claim 1, comprising up to 30 parts by weightof polycarbonate per 100 parts of thermoplastic polyester. 5.Compositions according to claim 1, wherein the copolymer (A) comprisesan elastomer core and one thermoplastic shell.
 6. Compositions accordingto claim 1, wherein the ethylene-unsaturated epoxide copolymers (B2) areethylene-alkyl(meth)acrylate-unsaturated epoxide copolymers obtained bycopolymerization of the monomers and contain from 0 to 40% by weight ofalkyl(meth)acrylate and up to 10% by weight of unsaturated epoxide. 7.Compositions according to claim 1, comprising, per 100 parts by weight,75 to 95 parts of polyester for 25 to 5 parts of impact modifier,respectively.